Electromagnetic shields are known. The electromagnetic noise generated by and emanating from digital controllers is known and has become more severe as the operating speed and relative complexity in terms of the requisite number of signal paths for such controllers continues to increase. The importance of such shields and shielding systems along with the severity of the effects of the electromagnetic noise have increased with the relative reduction in the physical size of underlying electronic assemblies. The advent of reduced size automated surface mount assembly technology has forced the electromagnetic shield to occupy a minimum amount of physical space while providing superb shielding, be assembly efficient, and of course economically effective.
Reduced size goals for the assembly mandates minimizing the size of all components and the space between components and subassemblies as well as minimizing part counts. As a result of these space reductions the degree of shielding required may have increased since circuits, such as digital controllers and receivers, that historically did not need to be especially well isolated may now have to be in order to operate satisfactorily. This has mandated that practitioners direct significant attention to increasing the effectiveness of while simultaneously reducing the effective size of such shields. Assembly efficiency ordinarily mandates minimal part counts with 1 component being favored over 2 components, etc. In addition automated assembly requires a regular shaped component that is easily and repetitively handled by mechanically actuated assembly arms and this favors relatively regular exterior surfaces with a minimal amount of assembly motion directed to orientation.
It is known to use electromagnetic shields that resemble an open sided box with the open side being placed on a carrier, however these shields may not provide sufficient shielding effectiveness, particularly when numerous signal paths must traverse the shield boundaries. This signal path problem may be resolved by using feed through capacitors electrically coupled to the sides of the box and providing connections to both terminals of the capacitor. However this is expensive, both in terms of the capacitors as well as the connections to both terminals of the capacitor plus normally proves to be prohibitively expensive and unwieldy to assemble.
Clearly a need exists for a cost effective electromagnetic shield for digital controllers that provides sufficient shielding effectiveness at a practical size and cost and consistent with the requirements of reduced size automated surface mount assembly operations.